1. Field of the Invention
The present invention relates to an atmosphere exchange method.
2. Description of the Related Art
A conventional load lock chamber imports a substrate from a substrate stocker that is placed in the atmosphere environment, into a processing chamber that processes the substrate in the vacuum atmosphere, or exports a processed substrate from the processing chamber to the substrate stocker. The processing chamber, as used herein, means a EUV (extreme ultraviolet) exposure apparatus and a plasma processing apparatus.
The load lock chamber serves to exchange an atmosphere in the internal space between the atmosphere environment and the vacuum environment. More specifically, the load lock chamber exchanges the atmosphere from the atmosphere environment to the vacuum environment in importing the substrate into the processing chamber (in the exhaust process), and exchanges the atmosphere from the vacuum environment to the atmosphere environment in exporting the substrate to the substrate stocker (in the air-supply process). The load lock chamber is connected to the processing chamber via a gate valve, and includes a substrate transport mechanism.
However, particles swirl from the gate valve and the substrate transport mechanism in the air-supply and exhaust time, and a means is necessary to reduce or prevent their adhesions to the substrate. One proposed method reduces particles' adhesions to the substrate utilizing the thermophoretic force. As disclosed in Japanese Patent No. 2,886,521, this method heats the holder of the substrate up to a temperature higher than the peripheral temperature, and collects particles via a low-temperature particle collector maintained at a temperature lower than the peripheral temperature.
According to the principle of the thermophoretic force, with a temperature gradient in the gas around the particles, the particles are given the kinetic energy from the gas molecules at the high temperature side higher than that of the gas molecules at the low temperature side, and move from the object at the high temperature side to the low temperature side. Thermophoretic force Fx is given by the following equation by the thermophoresis coefficient equation described in Kikuo Okuyama, Hiroaki Masuda, and Seiji Morooka, “New System Chemical Engineering, Fine Particles Engineering,” pp. 106-107, May of 1992, Ohmsha Publishing.
                    Fx        =                                                            -                6                            ⁢              π              ⁢                                                          ⁢                              D                p                            ⁢                              μ                2                            ⁢                                                C                  s                                ⁡                                  (                                      K                    +                                                                  C                        t                                            ⁢                                              K                        n                                                                              )                                                                                    ρ                ⁡                                  (                                      1                    +                                          3                      ⁢                                              C                        m                                            ⁢                                              K                        n                                                                              )                                            ⁢                              (                                  1                  +                                      2                    ⁢                    K                                    +                                      2                    ⁢                                          C                      t                                        ⁢                                          K                      n                                                                      )                                              ·                      1            T                    ·                                    Δ              ⁢                                                          ⁢              T                                      Δ              ⁢                                                          ⁢              x                                                          EQUATION        ⁢                                  ⁢        1            
Equation 1 assumes that the particle is spherical and the fluid is the ideal gas. Dp is a particle diameter. T is a gas temperature. μ is a viscosity coefficient. ρ is a gas density. Kn is a Knudsen number and 2λ/Dp. λ is a mean free path and η/{0.499 P(8M/πRT)1/2}. M is a molecular weight. R is a gas constant. K is k/kP. k is a thermal conductivity of the gas only caused by the parallel movement energy. kp is the thermal conductivity of the particle. Cs is 1.17. Ct is 2.18. Cm is 1.14. ΔT/Δx is a temperature gradient.
The dimension of the load lock chamber is restricted by the gate opening size (W360 mm×H80 mm) determined by the uniform standard in the semiconductor field, and cannot be made as small as the substrate's external shape. Therefore, the thermophoretic force near the substrate holder inevitably depends upon a shape of the load lock chamber, and thus cannot be maximized.